In nature, there are a lot of compounds containing a nitrogen atom(s). It has been considered that many 5-membered cyclic skeletons containing a nitrogen atom(s) among these compounds significantly contribute to exhibition of molecular functions. In particular, the compounds having a pyrazoline or pyrazolidine skeleton exhibit various biological activities, and these compounds are recently attracting attention as target chemical structures in the field of medicines, agrichemical, perfumes and the like. On the other hand, a lot of natural substances, for example proteins, are optically active compounds, and it has been known that they exhibit a specific biological activity according to their stereochemistry.
A useful process for preparing nitrogenous 5-membered cyclic skeletons is a [3+2] cyclization reaction. In particular, cyclization reactions using highly reactive 1,3-dipolar compounds such as nitrone have been widely studied. It has already been reported that optically active nitrogenous 5-membered cyclic skeletons are produced by catalytic asymmetric cyclization reactions (for example, Non-Patent Documents 1 and 2). These reactions, however, must be performed under strong acidic condition or heating conditions. It has not been known yet that cyclization reactions for preparing optically active 5-membered cyclic compounds having vicinal nitrogen atoms such as a pyrazoline or pyrazolidine skeleton can be achieved using a catalytic amount of a Lewis acid under a mild condition (for example, Non-Patent Documents 3 and 4).
The inventors of the present application have reported that the intramolecular cyclization reaction of a hydrazone can be achieved using a catalytic amount of zirconium triflate under a mild condition to afford a desired compound with high diastereoselectivity and in high yield (Non-Patent Document 5). However, application of this reaction is limited to some compounds, and the reaction is not versatile.
Non-Patent Document 1: Comprehensive Organic Synthesis; Trost, B. M. Ed.; Pergamon Press: Oxford, 1991: Vol. 5, Chap 3. 3.
Non-Patent Document 2: Gothelf, K. V.; Jorgensen, K. A. Chem. Rev. 1998, 98, 86
Non-Patent Document 3: Kanemasa, S.; Kanai, K. J. Am. Chem. Soc. 2000, 122, 10710;
Non-Patent Document 4: Shintani, R.; Fu, G, C. J. Am. Chem. Soc. 2003, 125, 10778.
Non-Patent Document 5: Kobayashi, S.; Hirabayashi, R.; Shimizu, H.; Ishitani, H.: Yamashita, Y.; Tetrahedron Lett., 2003, 44, 3351.
Non-Patent Document 6: Cox, P. J.; Wang, W.; Snieckus, V. Tetrahedron Lett. 1992, 33, 2253.
Non-Patent Document 7: Yamashita, Y.; Ishitani, H.; Shimizu, H.; Kobayashi, S. J. Am. Chem. Soc. 2002, 124, 3292.
Non-Patent Document 8: Kaya, R.; Beller, N. R. J. Org. Chem. 1981, 46, 196.